CARBONATE DISSOLUTION AND TEMPORAL ABUNDANCES OF FORAMINIFERA IN LONG-ISLAND SOUND SEDIMENTS

The dynamics of benthic Foraminifera assemblages can be used to examin e carbonate dissolution processes in nearshore sediments and as a gene ral assay of physical-chemical factors affecting survival of juvenile benthos. Abundances of total Foraminifera (live and dead) fluctuate re gularly throughout the year in Long Island Sound (LIS) mud deposits, w ith highest numbers in spring-summer and lowest in winter. Essentially all forams disappear each year. Pore-water undersaturation with respe ct to carbonate minerals coincides with periods of rapid disappearance of forams and suggests that these fluctuations reflect a balance betw een the rate of production-recruitment and the rates of death and diss olution of the calcareous tests of the animals. Reworking by macrofaun a in LIS central basin sediments inhibits accumulation or depletion of pore-water solutes and is responsible for minimizing pore-water carbo nate saturation states. Quantitative estimates of seasonal patterns of foram dissolution with a simple mass balance model give a minimum ave rage annual flux of Ca2+ in LIS sediments of approximately 6 mmol Ca2 m-2 d-1 (due solely to Foraminifera dissolution). Abandoned tests hav e a maximum mean residence time of approximately 86 +/- 13 d. Dissolut ion-precipitation of forams may significantly affect benthic SIGMACO2 fluxes and likely accounts for a large proportion (>30%) during some s easons or at some locales. Other organisms with carbonate tests of sim ilar size, particularly juvenile bivalves, may also be affected by per iods of undersaturated pore waters. Conditions promoting dissolution o f tests may represent an important source of mortality for calcareous meiofauna.